COVID-19 Evidence Alerts
from McMaster PLUSTM

Current best evidence for clinical care (more info)

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Quality Improvement, Primary Prevention Chou R, Dana T, Jungbauer R, et al. Masks for Prevention of Respiratory Virus Infections, Including SARS-CoV-2, in Health Care and Community Settings : A Living Rapid Review. Ann Intern Med. 2020 Oct 6;173(7):542-555. doi: 10.7326/M20-3213. Epub 2020 Jun 24.

BACKGROUND: Recommendations on masks for preventing coronavirus disease 2019 (COVID-19) vary.

PURPOSE: To examine the effectiveness of N95, surgical, and cloth masks in community and health care settings for preventing respiratory virus infections, and effects of reuse or extended use of N95 masks.

DATA SOURCES: Multiple electronic databases, including the World Health Organization COVID-19 database and medRxiv preprint server (2003 through 14 April 2020; surveillance through 2 June 2020), and reference lists.

STUDY SELECTION: Randomized trials of masks and risk for respiratory virus infection, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and observational studies of mask use and coronavirus infection risk were included. New evidence will be incorporated by using living review methods.

DATA EXTRACTION: One reviewer abstracted data and assessed methodological limitations; a second reviewer provided verification.

DATA SYNTHESIS: 39 studies (18 randomized controlled trials and 21 observational studies; 33 867 participants) were included. No study evaluated reuse or extended use of N95 masks. Evidence on SARS-CoV-2 was limited to 2 observational studies with serious limitations. Community mask use was possibly associated with decreased risk for SARS-CoV-1 infection in observational studies. In high- or moderate-risk health care settings, observational studies found that risk for infection with SARS-CoV-1 and Middle East respiratory syndrome coronavirus probably decreased with mask use versus nonuse and possibly decreased with N95 versus surgical mask use. Randomized trials in community settings found possibly no difference between N95 versus surgical masks and probably no difference between surgical versus no mask in risk for influenza or influenza-like illness, but compliance was low. In health care settings, N95 and surgical masks were probably associated with similar risks for influenza-like illness and laboratory-confirmed viral infection; clinical respiratory illness had inconsistency. Bothersome symptoms were common.

LIMITATIONS: There were few SARS-CoV-2 studies, observational studies have methodological limitations, and the review was done by using streamlined methods.

CONCLUSION: Evidence on mask effectiveness for respiratory infection prevention is stronger in health care than community settings. N95 respirators might reduce SARS-CoV-1 risk versus surgical masks in health care settings, but applicability to SARS-CoV-2 is uncertain.

PRIMARY FUNDING SOURCE: Agency for Healthcare Research and Quality.

Discipline / Specialty Area Score
Public Health
Intensivist/Critical Care
Pediatrics (General)
Family Medicine (FM)/General Practice (GP)
Emergency Medicine
General Internal Medicine-Primary Care(US)
Hospital Doctor/Hospitalists
Internal Medicine
Infectious Disease
Pediatric Emergency Medicine
Pediatric Neonatology
Occupational and Environmental Health
Pediatric Hospital Medicine
Comments from MORE raters

Emergency Medicine rater

Wear your mask!

Emergency Medicine rater

In the midst of a global pandemic, the extraordinary efforts to find and study strategies to prevent or treat COVID-19 have significantly challenged traditional journal editorial boards to provide meaningful peer-review of submitted research. One side effect has been the perception by some medical professionals that the tipping point of "peer-review" in favor of social media has been reached since podcasts and blog postings occur much more quickly than tedious editorial reviews behind "black curtains". Wearing masks is a prototypical example of this COVID-19 social media backlash - see AND This living review returns rigorous research methods and quality peer-review to counter increasingly prevalent perceptions that social media has become the defacto source for trusted medical "truth".

General Internal Medicine-Primary Care(US) rater

Like all PPE, wearing a mask is a variable process that is much more streamlined in health care settings than outside hospitals and clinics. This is a complicated heterogeneous topic of study and my recommendations to mask up, wash your hands, and keep your distance in the time of COVID doesn't change on the basis of this study.

Hospital Doctor/Hospitalists rater

This is a timely article with good methods that directly addresses many concerns and questions raised by patients, colleagues, and friends.

Infectious Disease rater

It must be understood by all readers that this is NOT a COVID-19 paper and should NOT be misunderstood to suggest that routine masking by the public when in close proximity to others is not recommended to prevent the spread of COVID-19. That is not addressed by this paper.

Infectious Disease rater

This is relevant but I’m not sure it's helpful.

Infectious Disease rater

Very good methodology but not enough evidence to make a definitive decision.

Intensivist/Critical Care rater

Please disseminate this widely and immediately. With the politicization of mask-wearing, all evidence supporting wearing masks must be clearly and relentlessly disseminated to counter false information, such as "You can get CO2 poisoning from wearing a mask" "Your oxygen levels can go down by 60% if you wear a mask."!

Intensivist/Critical Care rater

This is a difficult topic to report on because the effectiveness of masks is difficult to measure and quantify. This is, however, a good addition to the knowledge base and is a living document, which means that it is subject to change. Changing guidelines need to be viewed in that context as more data emerges.

Internal Medicine rater

I take this SR on mask effectiveness to be at odds with the conclusions of the Lancet SR on PPE published recently by Chu et al, and funded by WHO.

Occupational and Environmental Health rater

Despite the fact that many OM physicians are likely tracking articles on mask use, the inclusion of an evidence map was a particularly useful way to quickly review the overall data. For that reason, this is a useful review.

Pediatric Neonatology rater

A meta-analysis that is based on a poor studies. Very few RCTs and they indicate that in those mask compliance was limited. This is a critical question, but it`s hard to do an RCT of mask vs no-masks for HCW in a high-risk situation (e.g., a COVID-19 unit). Thus, all this article does is illuminate our incomplete data. I still recommend wearing a mask.

Pediatrics (General) rater

Good review of studies of masks to prevent COVID and other respiratory infections.

Public Health rater

Covid-19 is spread primarily through contact with large respiratory droplets, and possibly through finer respiratory aerosols. Several types of face masks are available. Disposable N95 face masks are fitted and have been tested to show very high levels of blocking small airborne particles including aerosols. Surgical and medical masks are loose fitting and create a physical barrier to block large particles. Cloth masks are non-medical face coverings that vary in levels of fluid and in filtration efficiency and fluid resistance. This review is of 39 reports (18 were RCTs). As would be expected, study quality varied. Mask comfort was not specifically evaluated. Clearly, all masks are uncomfortable and are frequently removed by users (dangling from their necks). Nonetheless, the article is of interest and does remind readers of the variable mask efficiency in blocking larger airborne respiratory particles.